1. Field of the Invention
The present invention relates to a combined cycle power plant that can generate power not only with driving a gas turbine but also with using heat of an exhaust gas from the gas turbine and driving a steam turbine.
2. Description of the Related Art
At this time, from a viewpoint of a resource saving and environment protection a combined cycle power generation that improves a power generation efficiency with combining a gas turbine and a steam turbine that uses exhaust heat thereof is used. A combined cycle power plant that employs the combined cycle power generation is configured by combining the gas turbine, the steam turbine, a heat recovery steam generator, and the like. If the gas turbine is driven, it is designed that an exhaust gas exhausted from the gas turbine is introduced into the heat recovery steam generator, and that the steam turbine is driven with steam produced by the heat recovery steam generator.
But when starting up the combined cycle power plant and directly introducing an exhaust gas of a high temperature exhausted from the gas turbine into the heat recovery steam generator, for example, strains might occur to cause breakage in pipes of the heat recovery steam generator due to a drastic heat input by the exhaust gas. Therefore, in order to prevent the breakage of the heat recovery steam generator, generator, a method of controlling an output of the gas turbine while suppressing the output is adopted there is a problem in that the method that it takes very long time but, for the output of the gas turbine to be raised to a rated load thereof and power taken out. Consequently, a solution for problem is disclosed in paragraphs 0020 to 0028 and FIG. 1 of Japanese Patent Laid-Open Publication Hei. 7-83401 (hereinafter referred to as “patent document 1”).
In the technology described in the patent document 1, between a gas turbine and a heat recovery steam generator is provided a bypass stack for bypassing the heat recovery steam generator, and at inlet sides of the heat recovery steam generator and the bypass stack are provided dampers, respectively. In starting up a plant a damper opening of the heat recovery steam generator is set full close, that of the bypass stack is set full open, the gas turbine becomes a rated load operation, and thereafter the damper opening of the heat recovery steam generator is controlled so as to gradually become larger and that of the bypass is controlled so as to become smaller. Thus by providing the damper between the gas turbine and the heat recovery steam generator and making a drastic heat input not occur for the heat recovery steam generator, it is designed that a problem such as a breakage of the heat recovery steam generator can be prevented. In addition, similar damper structures are described in paragraph 0039 and FIGS. 1 and 3 of Japanese Patent Laid-Open Publication Hei. 8-75103 (hereinafter referred to as “patent document 2”), and in paragraph 0012 and FIG. 1 of Japanese Patent Laid-Open Publication Hei. 7-91602 (hereinafter referred to as “patent document 3”).
But in suggestions of providing a damper described in the patent documents 1 to 3, because an exhaust gas of a very high pressure is blown into the damper, there is a possibility that only if the damper is simply supported, it fiercely vibrates due to a wind pressure, a strong force acts on such a damper drive for supporting the damper, and thus is damaged. Accordingly, in order not to damage the damper, it is necessary, for example, to form the damper drive, which supports the damper, of a high strength material or to make the damper drive such one that produces a strong motivity as a driving force transmitted to the damper.
In addition, by a vibration occurring in a damper, it becomes unable to highly accurately control an introduction amount introduced into a heat recovery steam generator and a bypass amount of an exhaust gas bypassing the heat recovery steam generator: there is also a possibility that a drastic heat input is produced for the heat recovery steam generator, and that the heat recovery steam generator is damaged.
Furthermore, as a conventional heat recovery steam generator, although a natural circulation type is adopted, it has a drum of a very large thickness: an excessive thermal stress occurs due to a drastic heat inflow; it is necessary to suppress a load up rate in an operation of a damper; and as a result there is such a problem that a start-up time becomes longer.
Consequently, it is strongly requested a combined cycle power plant that can control a damper in high accuracy and widely shorten a start-up time without increasing manufacturing cost thereof.